//根据圆的半径
var p =Math.PI;
var bj = prompt("请输入圆的半径");
//圆的周长 = 直径 × π = 2 × 半径 ×π
var zc = 2 * bj * p;
//圆的面积 = 半径的平方 × π = π × 半径 × 半径
var mj =p * bj * bj;
document.querySelector("#a").value = bj;
document.querySelector("#b").value = zc;
document.querySelector("#c").value = mj;

